Lecithin is commonly added to cooking fats as an anti-sticking agent, but has the disadvantage that it darkens in color at high temperatures, thereby limiting the level which can be used. Foodservice establishments are often required to hold a heated fat for extended periods of time. Fats containing a higher than normal level of lecithin to enhance the anti-sticking properties darken more quickly when subjected to continuous heating. Associated with this discoloration is generation of an off-flavor. The increased darkening and generation of off-flavor render such fats unacceptable. An effective means of preventing the darkening of lecithin at high temperatures is desirable and would permit its use at increased levels in fats to improve their anti-sticking performance.
Fat or oil additives known for inhibiting darkening of phospholipids, such as lecithin, upon heating are primarily acidic or weakly basic compounds such as amino acid salts, carboxylic acids and derivatives, or salts of carbonates or bicarbonates. inhibition of discoloration of phospholipids in fatty oils during heating can be achieved by the addition to the oil of a mixture of an acidic amino acid salt and a basic amino acid salt chosen from salts of arginine and glutamic acid, lysine and glutamic acid, or lysine and aspartic acid. Restraint of phospholipid coloration upon heating also results from the addition of sodium glutaminate, sodium succinate, or succinic acid to the fat. In addition, acetic anhydride or alkali metal acetate can be employed. Carbon dioxide-generating compounds also inhibit thermal darkening of fats containing phospholipids. Japan Pat. No. 107,530 of Matsueda et al., issued Aug. 23, 1979, discloses the use of a carbon dioxide-generating compound comprising the carbonates of potassium, ammonia, and magnesium, and bicarbonates of ammonia and sodium, added to the fat and lecithin mixture at a minimum level of 5% by weight, preferably 20% by weight, of the phospholipid. It is suggested that the carbon dioxide gas generated by heating for ten minutes at 150.degree. C. (302.degree. F.) or higher contributes to decreased discoloration. Japan Pat. No. 110,210 of Matsueda et al., issued Aug. 29, 1979, discloses a barbecue oil composition containing vegetable oil, a phosphatide, and a compound that generates carbon dioxide upon heating. The latter inhibits spattering and coloration upon heating of the barbecue composition.
Pretreatment of lecithin to prevent thermal browning in heated fat compositions is taught by Japan Pat. No. 54,400, issued Apr. 21, 1980. The pretreatment comprises heating the lecithin in an inert atmosphere, either alone or diluted with a fat, at 150.degree. C. to 230.degree. C. (302.degree. F. to 446.degree. F.) for five minutes to one hour.
The fact that weak bases inhibit thermal darkening of fats containing lecithin suggests that a strong base would be ineffective. Commercial lecithin usually contains carbohydrate substances such as short chain polysaccharides and oligosaccharides. These substances are also contained in many foods. Treatment of lecithin with a strong base in the presence of saccharides would be expected to increase darkening due to isomerization of the saccharide and even decomposition of the chain. It is unexpected that treatment of lecithin with a strong base would decrease darkening when used in cooking fats.
It has now been found that fat compositions containing lecithin and a strongly basic compound resist excessive thermal darkening. Treatment of the fat or lecithin with a strongly basic compound stabilizes the lecithin and prevents excessive discoloration of fats containing lecithin when heated. Strong bases such as sodium hydroxide, magnesium hydroxide, potassium hydroxide, and the like, are most effective. Thus, it is probably not the generation of carbon dioxide gas during heating that contributes to decreased discoloration of fats containing phospholipids, but instead the basic properties of the additive employed. The use of a low level of a strong base is advantageous in that the storage stability and the taste of the fat are not adversely affected. The preferred high levels of carbon dioxide generating compounds of Matsueda et al. would not be expected to contribute to enhanced storage stability or taste.
Accordingly, it is an object of this invention to provide novel fat compositions which resist thermal darkening.
It is a further object of this invention to provide novel processes for stabilizing lecithin to prevent excessive darkening of fats containing lecithin upon heating.
It is a further object of this invention to provide a process for the pretreatment of lecithin that will aid in decreasing its thermal discoloration in heated fats.
These and other objects of the invention will be evident from the following disclosure. All percentages are by weight unless otherwise indicated.